In a semiconductor manufacturing process for a semiconductor device, for example, multiple substrates to be processed (e.g., semiconductor wafer) are accommodated in a cassette while having a gap therebetween in a vertical direction, and are unloaded from the cassette by a transfer robot one by one and transferred to a processing chamber. Meanwhile, prior to this, a detection may be made as to whether or not a substrate is present in the cassette for each support level. As an example of a device for performing such a detection (generally, referred to as a mapping device), there is a conventional substrate detecting device using a transmission type optical sensor (for example, see Japanese Patent Laid-Open Application No. 2000-36528).
FIGS. 9 and 10 are of a plane view and a side view schematically showing the conventional substrate detecting device (mapping device) 20 disclosed in the aforementioned Laid-Open Application No. '528, respectively. The substrate detecting device 20 includes a sensor support body 21 mounted on a substrate transfer robot 30. The sensor support body 21 has a pair of arms 21A and 21B placed spaced apart but extending facing each other in a horizontal plane. Two sets of optical sensors 22 and 23 are disposed between the pair of arms 21A and 21B of the sensor support body 21. The respective optical sensors 22 and 23 are formed of combinations of the light emitting units 22A and 23A and the light receiving units 22B and 23B. The light emitting units 22A and 23A are placed in one end of arm 21A while the receiving units 22B and 23B are placed in an analogous location of arm 21B. One set of the optical sensor 22 is disposed at front ends of the arms 21A and 21B, and the other set of the optical sensor 23 is disposed at inner sides thereof.
In the respective optical sensors 22 and 23, light beams are horizontally irradiated from the light emitting units 22A and 23A to the light receiving units 22B and 23B, and based on transmitted light receiving signals of the light receiving units 22B and 23B, it is determined whether or not there exists a light blocking object (in this case, substrate) in the paths of the light beams. The light beams of the optical sensors 22 and 23 are irradiated in parallel while having a predetermined interval therebetween in the entering direction of the arms 21A and 21B into the cassette C, i.e., forward/backward direction of the cassette C. The front side optical sensor 22 determines whether or not there exists a substrate W, and the alternate side optical sensor 23 detects whether or not the substrate W is protruding from the cassette C by a predetermined distance or more.
For positioning, by inserting the tip ends of the pair of arms 21A and 21B of the sensor support body 21 from a substrate entrance of the front side thereof into the cassette C, a positioning mechanism 24 formed of a linearly moving actuator is installed. A driving mechanism for scanning is installed to scan the light beam along a vertical direction by vertically moving the sensor support body 21 while the pair of arms 21A and 21B are placed in the cassette C. A control operation section is installed to determine the presence or absence of the substrate W at each support level of the cassette C, and to determine a protrusion level thereof by a predetermined distance or more, based on the light receiving signals of the optical sensors 22 and 23 obtained at each scanning position. Since the substrate detecting device 20 is mounted on the transfer robot 30, the driving mechanism for scanning which is capable of vertically moving the sensor support body 21 is also used as an elevation driving section for the transfer robot 30.
In order to carry out substrate detection in the cassette C by the substrate detecting device 20, the sensor support body 21 is moved toward the cassette C by the positioning mechanism 24. Then, the tip ends of the pair of arms 21A and 21B of the sensor support body 21 are placed into the cassette C, so that they are positioned at a reference position ready for substrate detection. Subsequently, by operating the elevation driving section at that stage, the sensor support body 21 is lowered and moved to a lowest support level of the cassette C. Thereafter, the sensor support body 21 is elevated from the lowest support level to a highest support level of the cassette C at a constant speed while operating the optical sensors 22 and 23.
Based on the data of the scanning positions and of the signals of the optical sensors 22 and 23, it can be determined at each support level whether or not there exists a substrate W and the existing substrate W is protruded. From the data on the presence or absence of the substrate W, the controller of the substrate transfer device places a pick (a substrate supporting unit) 25 of a transfer arm end of the transfer robot 30 in the cassette C to unload one by one therefrom the substrates W. More precisely, the pick 25 is inserted only into such locations where substrates W are not protruded and unloads the substrates W from any of such locations.
As mentioned above, the transfer robot for performing the unloading of substrates places a substrate on the pick from the cassette, and then, transfers the substrate to the next position. If the pick is of a type that only rests a substrate on its top face, the substrate may be dropped when the speed of the transfer robot's arm is increased. Thus, a pick with an alternative design which has multiple tapered protrusions disposed on the top surface of the pick main body can be employed for placing thereon the edge of the substrate (e.g., see Japanese Patent Laid-open Application No. 2002-26108 (FIGS. 5 and 6 thereof)).
FIGS. 11A through 11C show the picks of the transfer arm disclosed in the aforementioned Laid-Open Application No. '108; FIGS. 11A and 11B are a plane view and a side view thereof, respectively, and FIG. 11C is a side view showing an instance where the substrate is incorrectly mounted. As shown in FIGS. 11A and 11B, multiple protrusions 41s, each having a tapered surface 41a, on which the outer peripheral edge of the substrate W sits, are protrudingly disposed on the top surface of the pick main body 40 along the outer periphery of the substrate W. In case of using such a pick, the edge placement of the substrate W is restricted by each protrusion 41, so that the substrate W does not slip and fall off from the pick even though the speed of the arm in the transfer robot is increased. Further, by using such a pick, it is possible to correct the misalignment of the substrate W by the tapered protrusions 41. Namely, even though the substrate W is misaligned to a degree, such misalignment of the substrate W can be corrected as the substrate W is placed on the tapered surface 41a of the tapered protrusion 41.
However, when such a pick is used, if the position of the substrate W is misaligned so that its edge sits off the tapered surface 41a, as shown in FIG. 11C, it is possible that the substrate W be placed on top of the protrusion 41.
As for the position of the substrate W in the cassette C, it generally depends on the cassette C type or substrate W setting errors. Therefore, it is difficult to pick up the substrate while matching the center of the substrate with that of the pick all the time. Accordingly, for correcting a misalignment of the substrate, the transfer robot receives the substrate from the cassette, and transfers it to a position correction device called an orienter. After correction the misalignment by the orienter, the transfer robot receives the substrate back and loads it into the processing apparatus.
To increase the transferring speed, it is supposed that a pick capable of preventing a drop is employed, as shown in FIGS. 11A and 11B. In this case, if the degree of misalignment between the substrate and the pick falls outside a tolerance range, the condition as shown in FIG. 11C results. In that condition shown in FIG. 11C, if the substrate is transferred at a high speed, the substrate falls off from the pick.
Using the conventional substrate detecting device, while it is capable of determining the presence and the protrusion degree within a predetermined range or more of a substrate at each support level, it is unable to detect an exact position of the substrate in forward/backward direction thereof. For example, with respect to the substrate detecting device described in FIG. 9, it detects whether or not there exists a substrate W by using the front side (anterior side) optical sensor 22, and using the rear optical sensor 23, it detects whether or not the substrate W is protruding by a predetermined range or more. In this case, it is impossible to determine the position of the substrate with high accuracy.